A honeycomb structure has broadly been used as a filter for collecting dust from an exhaust gas, for example, a diesel particulate filter (DPF) for trapping and removing a particulate matter (particulates) such as soot included in the exhaust gas from a diesel engine or the like.
The honeycomb structure for use in such a purpose is exposed to the rapid temperature change of the exhaust gas or locally generated heat to easily generate a non-uniform temperature distribution in the structure, and this causes a problem that cracks are generated and the like. To solve such problems, a method has been suggested in which the honeycomb structure is constituted of a plurality of honeycomb segments, and the honeycomb segments are integrally joined together by use of a joining material constituted of an elastic material, whereby a thermal stress exerted on the honeycomb structure is relaxed (see Patent Document 1).
The honeycomb structure (a honeycomb segment joined body) constituted by joining the plurality of honeycomb segments together is usually prepared by arranging a plurality of honeycomb segments 30 in directions parallel to a first flat surface 21 and a second flat surface 22 of an installation reference jig 20 to install the segments in predetermined positions via a paste-like joining material 29 on the installation reference jig 20 by use of the jig having two flat surfaces (the first flat surface 21 and the second flat surface 22) forming a right angle therebetween as shown in FIG. 5, and then drying and curing the joining material 29. The first flat surface 21 and the second flat surface 22 are provided with pads 23 which come in contact with the honeycomb segments 30 if necessary. It is to be noted that in the example of FIG. 5, the first flat surface 21 of the installation reference jig 20 is parallel to a horizontal direction, and the second flat surface 22 is parallel to a vertical direction. However, as shown in FIG. 6, the installation reference jig is sometimes used so that each of the first flat surface 21 and the second flat surface 22 forms an angle of 45° with respect to a horizontal plane (e.g., see Patent Document 2).
FIG. 7 shows an ideal installation state after completely installing all the honeycomb segments in a case where 16 honeycomb segments 1 to 16 in total are installed in four rows along the direction parallel to the first flat surface 21 and four rows along the direction parallel to the second flat surface 22. The honeycomb segments 1 to 16 are thus arranged at equal intervals without being displaced, and the whole shape is adjusted in the ideal state. It is to be noted that the reference numerals 1 to 16 attached to the honeycomb segments in the drawing indicate an installation order. It is most general that the honeycomb segments are successively installed in a staircase pattern from the honeycomb segment 1 to be first installed to the honeycomb segment 16 to be last installed in this manner.
However, in a case where the honeycomb segments are actually installed by the above method, it is difficult to obtain the ideal installation state shown in FIG. 7, and a state is easily generated in which the honeycomb segments are displaced as shown in, for example, FIG. 8. This is because when a new honeycomb segment is installed in a predetermined position, the new honeycomb segment generates a pressurizing force with respect to the already installed honeycomb segment. That is, the joining material 29 present between the honeycomb segments finally dries and cures owing to a heating treatment or the like to firmly join the honeycomb segments together. However, during the installation of the honeycomb segments, the joining material is a paste-like material having fluidity, and the installed honeycomb segment has a floating state on the joining material 29, and is easily displaced owing to the fluidity of the joining material 29 at a time when an external force is applied.
As shown in an example of FIG. 8, the honeycomb segments 1 to 4, 6, 7 and 10 installed so as to come in contact with the pads 23 of the installation reference jig 20 are hardly displaced owing to frictional resistance to the pads 23, but the other honeycomb segments are easily displaced in a case where the new honeycomb segment is installed as described above. This displacement increases, as the number of the segments to be installed increases and the number of times when the already installed segment is pressurized by the newly installed segment increases.
For example, in FIG. 8, the honeycomb segment 13 is pressurized twice at a time when the honeycomb segment 15 is installed and a time when the honeycomb segment 16 is installed, so that considerably large displacement is easily generated. The honeycomb segment 15 is pressurized only once at a time when the honeycomb segment 16 is installed, and hence the displacement is smaller than that of the honeycomb segment 13. The honeycomb segment 11 is pressurized twice at a time when the honeycomb segment 14 is installed and a time when the honeycomb segment 16 is installed, so that the considerably large displacement is easily generated in the same manner as in the honeycomb segment 13.
Patent Document 1: JP 2000-279729 A
Patent Document 2: JP 2000-7455 A